Yellow Fever (YF), which is caused by YF virus (YFV), afflicts about 200,000 individuals yearly mostly in sub-Saharan Africa and to a lesser extent in the tropical regions of South America. YF is considered a reemerging threat and there is particular concern that South and Central America are ripe for future devastating epidemics. Dengue Fever (DF), which is caused by one of four dengue viruses (DENs), is a major and resurging health problem in tropical and sub-tropical countries. A conservative estimate of the population at risk is a staggering 2.5 billion people. DF can progress to dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), which are dreaded developments. All of these considerations conspire to make YF and DF, major and growing world health problems. Additionally these viruses represent a threat to the U.S. population, something made evident by the recent national outbreak of the related West Nile virus. The long-term problem addressed by this application is the fact that the illnesses caused by YF and DF (and other flaviviruses) currently have no cure. It is important, therefore, to develop novel therapeutics for these two viruses. The overarching goal of this application is to discover new potential therapeutic targets by identifying novel interactions between host proteins and viral RNAs. In order to accomplish this we propose the following specific aims: 1) To use RNA affinity chromatography and proteomic analysis to identify host proteins that specifically interact with important viral RNA elements. This aim will require experimental confirmation of RNA structures and elements, construction and testing of RNA affinity matrices, and proteomic analysis of specific interacting proteins. 2) To validate the functional importance of the identified RNA binding proteins. We will use molecular genetics and RNA interference to identify, among the viral RNA binding proteins, the factors required for YFV and DEN propagation. Successful completion of this exploratory project will permit us to develop a hypothesis-driven set of investigations to address the molecular details of these viral RNA-host protein interactions and their feasibility as therapeutic targets. The long-term public health problem addressed by this application is the fact that the illnesses caused by Yellow Fever and Dengue Fever viruses, and related viruses (e.g., West Nile Fever virus) currently have no cure. The overarching goal of this application is to discover new potential therapeutic targets by identifying novel interactions between components of the virus (RNA) and cellular factors. We hope this work will lead to the development of new antiviral therapies. [unreadable] [unreadable] [unreadable]